Fluids are commonly transported across large distances through pipelines formed of discrete pipe sections connected together end to end. In the transportation of hydrocarbons between off-shore facilities and on-shore processing plats, the pipelines can extend for many hundreds or in some cases thousands of miles. Before any fluids can be transported, the pipeline must be laid across the seabed.
One known system of pipe laying which is commonly employed in the construction of deepwater pipelines or riser systems is a J-laying method. Lengths of pipe are stored on a floating vessel. The pipeline is supported in a vertical or near vertical orientation on the vessel and extends from the vessel to the seafloor where it rests on the seabed. Each new pipe is transferred into a vertical orientation where it is welded onto the top-most pipe and the pipe string is lowered to bring the top of the new pipe into position for connection of a further pipe. In this system a mechanical device is incorporated for restraining the tension in the pipe catenary between the lay ship and the seabed.
Due to the very high tensions encountered in deepwater pipe laying, it is often necessary to provide a raised shoulder on the pipe end to be supported by the restraining device to prevent slippage. It is customary to use so-called J-lay collars for this purpose and typically these are machined from a forging or heavy wall section of pipe and then welded to the pipe to be supported. The collar supports the weight/tension in the pipe between the installation ship or platform and the seabed.
Since the J-lay collars remain as permanent items on the completed pipeline, they must conform to specified metallurgical, mechanical and structural integrity requirements that are similar or exceed to the pipeline material itself.
Attainment of these desired properties can be problematic and particularly when very heavy wall thickness, high strength and/or special corrosion resistant alloy materials are needed.